Tentorial Meningiomas
Case 4: Combined Transpetrosal Approach (Fig. 9.5)
A 39-year-old man presented with a 2-month history of gait disturbance. MR imaging showed a large mass lesion at the right tentorial incisura.
The tumor severely compressed the brain stem and medial temporal lobe. Resection of the tumor was performed via a combined transpetrosal approach. The tumor adhered tightly to the mid- brain at the interpeduncular cistern, leaving a small residual amount of tumor along the right
oculomotor nerve. Subtotal resection of the tumor was performed with transient right oculo- motor nerve palsy and left hemiparesis. These symptoms improved completely within 3 months.
Falcotentorial Type
Meningiomas arising from the falcotentorial junction are relatively rare, and only isolated case reports or small series related to surgical
Fig. 9.2 Case 1. Preoperative axial (a) and coronal (b) T1-weighted magnetic resonance images with gadolinium showing the left incisural type of tentorial meningioma.
Postoperative axial (c) and coronal (d) T1-weighted mag- netic resonance images with gadolinium showing no tumor residual via a retrosigmoid approach
Fig. 9.3 Case 2. Preoperative axial (a) and coronal (b) T1-weighted magnetic resonance images with gadolinium showing the left incisural type of tentorial meningioma.
Postoperative axial (c) and coronal (d) T1-weighted mag- netic resonance images with gadolinium showing near- total resection of the tumor via a retrosigmoid approach with drilling of the petrous bone. After internal debulking
of the tumor (e), the left SCA is exposed (f). The tumor is peeled from the brain stem (g), and the petrous apex is drilled out (h). The tumor in Meckel’s cave is removed (i), and most of the tumor is resected, except for just around the porous part of the trochlear nerve (j). SCA superior cerebellar artery
Fig. 9.3 (continued)
Fig. 9.4 Case 3. Preoperative axial (a) and coronal (b) T1-weighted magnetic resonance images with gadolinium showing the left incisural type of tentorial meningioma.
Postoperative axial (c) and coronal (d) T1-weighted mag- netic resonance images with gadolinium showing total removal of the tumor via an anterior transpetrosal approach. After opening of Meckel’s cave (e), internal
debulking of the tumor is performed. The tumor is care- fully peeled from the trochlear nerve (f), and the tento- rium is detached from the tumor (g). The tumor located around the trigeminal nerve and brain stem is removed (h). Residual tentorium, which was the origin of the tumor, is resected completely (i), and the tumor is totally removed (j)
Fig. 9.4 (continued)
Fig. 9.5 Case 4. Preoperative axial (a) and coronal (b) T1-weighted magnetic resonance images with gadolinium showing the large right incisural type of tentorial menin- gioma. Postoperative axial (c) and coronal (d) T1-weighted magnetic resonance images with gadolinium showing near-total resection of the tumor via a right combined transpetrosal approach. After cutting of the superior petrosal sinus (e) and opening of Meckel’s cave, internal
debulking of the tumor is performed (f, g). The proximal portion of the right SCA is exposed (h). The distal portion of the right SCA and brain stem are peeled from the tumor (i). Near-total resection of the tumor is achieved with a small residual tumor along the right oculomotor nerve (j).
SPS superior petrosal sinus, SCA superior cerebellar artery, * residual tumor
Fig. 9.5 (continued)
Fig. 9.6 Illustration demonstrating the type of tumor by location. A tumor located over the vein of Galen and com- pressing it downward is classified as the superior type (a),
and one situated under the vein of Galen and dislocating it upward is the inferior type (b)
technique are available in the literature [1, 3].
Because of the lesion’s depth from the surface and its anatomical proximity to critical neural and vascular structures, surgical access and technique are complex issues. A variety of fac- tors, including the tumor location and the patency of the vein of Galen and the straight sinus, influ- ence surgery and the outcomes. Falcotentorial meningiomas are difficult to treat, but they can be well controlled by meticulous strategy.
Surgical Planning
Preoperative neuroimaging investigations include MR imaging, MR venography, CT venography, and angiography. Apart from evaluating the physi- cal characteristics of the tumor, the relationship of the tumor to the great vein of Galen, the patency of the vein of Galen and the straight sinus are evalu- ated, and pre-existing occlusion of the Galenic system and the subsequent development of collateral venous circulation are important factors when considering surgery on pineal region tumors, including falcotentorial junction meningiomas [3].
Depending on the relationship of the tumor to the great vein of Galen, tumors are classified into
two types: tumors located superior to the vein and compressing it downward are labeled the superior type, whereas those displacing it superi- orly are labeled the inferior type (Fig. 9.6).
The superior type of falcotentorial meningi- oma growing inside the posterior pericallosal cis- tern might compress deep veins over the arachnoid membrane. In this situation, a thick arachnoid membrane septum between the poste- rior pericallosal cistern and the quadrigeminal cistern protects the deep veins from direct tumor invasion, which enables the surgeon to dissect the lesion from the deep veins. Therefore, in the case of superior type tumor, even when the vein of Galen is patent, careful surgical technique enables the surgeon to separate the tumor from the vein of Galen. Thus, complete surgical removal can be relatively safely performed in the case of superior type tumors.
The inferior type of falcotentorial meningi- oma growing in the quadrigeminal cistern might compress the deep veins and dorsal midbrain in direct contact with it. Accordingly, in many cases of inferior type, the tumor adheres tightly to the vein of Galen, basal vein, collateral veins, and midbrain. In cases of inferior type tumor with an occluded Galenic system, dissecting the
tumor from surrounding collateral veins and brain stem is relatively difficult technically.
Resection of the tumor in such cases leads to damage of the surrounding structures with addi- tional neurological deficits. In cases in which the Galenic venous system is patent, the surgical procedure is more difficult because the tumor adheres tightly to the venous system. To prevent injury to the deep veins, a small amount of the tumor can be left behind around the deep veins to avoid their injury in the context of an inferior type tumor. Considering the surgical risk involved in excising the inferior type of menin- gioma, a combination of subtotal tumor resec- tion and stereotactic radiotherapy might be recommended.
As a surgical strategy, the superior type tumor is accessed using a posterior interhemi- spheric transtentorial approach, and there may be some who prefer a posterior interhemispheric transtentorial approach for inferior type tumors.
With inferior tumors located below the vein of Galen, a supracerebellar approach might be advantageous because the vein of Galen would not be directly in harm’s way. Surgeons would not have to work through the vein and its tribu- taries. Therefore, a supracerebellar infratento- rial approach to inferior type tumors should be considered [3].
Illustrative Case
Case 5: Posterior Interhemispheric